Characteristics of a terrible investment
Anything that involves leverage: Leverage is employing debt capital to increase returns; added leverage drastically increases the risk of an investment.
CFD's: Contracts for difference are NOT INVESTMENTS, despite what some hedge funds may advertise. CFD's involve leverage and margin, and can only be used as responsibly for hedging. As investors, stay away from these at all costs; they are gambling instruments and can become very addictive. The predatory companies who offer these advertise heavily, and paint a false picture of responsibly trading.
A non productive asset: these are 'assets' that don't offer any return, nor produce anything. Consider cryptocurrencies; they don't offer a yield, nor do they produce anything that will provide a return on investment. Your only hope is that someone pays you more for it in the future than your purchase price. This isn't investing, it's stupidity. Commodities fit this description as well; buying commodities in the hope of price appreciation isn't investing, as these commodities don't provide a return on investment.
A euphoric share price: Investing isn't just about buying shares in the best company, what matters almost as much is the price you pay for them. A company can have inpentrable barriers to entry and gargantuan growth prospects, yet if one overpays for it, it's a terrible investment. A share price become euphoric when taxi drivers and your average bloke at the pub starts talking about it's certainty.